1. Field of the Invention
The present invention relates to a pump for supplying a fuel to a two cycle engine or a four cycle internal combustion engine, in general, to the two cycle engine, and more particularly to a pulsation type diaphragm pump which is driven by a pressure pulsation generated within a crank case or within an intake manifold in accordance with an operation of the engine.
2. Description of the Conventional Art
A mixture at a predetermined rate of air and fuel produced by a carburetor placed in an intake passage extending to a combustion chamber of the engine from an air cleaner is supplied to a two cycle or four cycle compact internal combustion engine as a power source for a farm machine, an outboard motor, a light car or the like. As a pump for feeding a fuel in a fuel tank to the carburetor, there is widely used a pulsation type diaphragm pump having advantages such as a simple structure in comparison with a mechanical or electromagnetic pump and a characteristic of being driven with no mechanical loss.
An embodiment of an arrangement among the air cleaner, the carburetor, the two cycle engine and the pulsation type diaphragm pump is described in Japanese Utility Model Publication No. 97317/1977. Further, a detailed explanation of the pulsation type diaphragm pump is described in pages 36 to 40 of a bimonthly xe2x80x9cCar Technologyxe2x80x9d issued by Tetsudo-Nihon-Sha, Tokyo, Japan on January 1983.
FIG. 7 is a vertical cross sectional view showing the same structure as a typical pulsation type diaphragm pump described in the above bimonthly. A pump diaphragm 52 and a cover body 53 are laid over one surface of a main body 51 of the pump, and a recess provided in the main body 51 and covered by the pump diaphragm 52 forms a pump chamber 54. An inner portion of the cover body 53 partitioned from the pump chamber 54 by the pump diaphragm 52 forms a pulse chamber 55, and a diaphragm spring 57 is received in the pulse chamber 55.
A pulsator diaphragm 58 and a cap 59 are laid over another surface of the main body 51, and two recesses provided in the main body 51 to be back to back with the first mentioned recess and covered by the pulsator diaphragm 58 form an intake chamber 60 and a discharge chamber 62 respectively. An inner portion of the cap 59 partitioned from the intake chamber 60 and the discharge chamber 62 by the pulsator diaphragm 58 form air chambers 64 communicated with an atmospheric air. Further, an intake valve 65 is provided between the intake chamber 60 and the pump chamber 54, and a discharge valve 67 is provided between the pump chamber 54 and the discharge chamber 62.
A pressure pulsation within a crank case or within an intake manifold generated in accordance with an operation of an engine, in general, a pressure pulsation within the crank case is introduced to the pulse chamber 55 from a pulse introduction port 56 provided in the cover body 53 so as to oscillate the pump diaphragm 52 in cooperation with the diaphragm spring 57. A fuel stored in a fuel tank (not shown) flows from a fuel inlet 61 to a fuel outlet 63 through the intake chamber 60, the intake valve 65, the pump chamber 54, the discharge valve 67 and the discharge chamber 62 due to an operation of the diaphragm 52 so as to be fed to a carburetor (not shown). The pulsator diaphragm 58 serves to smoothen the pulsation of the fuel in the intake chamber 60 and the discharge chamber 62 so as to improve an intake efficiency and a discharge efficiency.
The intake valve 65 and the discharge valve 67 are check valves placed on a bottom wall 51a which sections between the pump chamber 54 of the main body 51 and the intake chamber 60 and between the pump chamber 54 and the discharge chamber 62 respectively. There are provided with valve seat ports 66a and 68a communicating the intake chamber 60 with the pump chamber 54 and the pump chamber 54 with the discharge chamber 62 respectively on the bottom wall 51a, and are structured such that bevel-shaped valve bodies 66b and 68b made of an elastic material are mounted on the bottom wall 51a so as to open and close the valve seat ports 66a and 68a respectively.
On the other hand, the pulsation type diaphragm pump is generally compact, and a diameter of the pump diaphragm 52 is ordinarily less than 10 cm. Accordingly, the valve bodies 66b and 68b of the intake valve 65 and the discharge valve 67 placed within the pump are significantly small, and there is a case that the valve seat ports 66a and 68a are hardly bend and deform largely enough to open largely so that a fuel flow amount required by the engine is secured.
As the intake valve and the discharge valve, there has been known a valve with a valve body being formed in a linearly oscillating plate shape instead of a bevel shape bending and deforming at an outer peripheral edge portion. This valve body can largely open the valve seat port. However, most of such valve bodies are provided with a closing valve spring for completely closing the valve and a spring receiver for holding the closing valve spring in cooperation with the valve body, in addition to a guide for linearly oscillating the valve body. Accordingly, the number of parts constituting the pump is large and all of these parts have small sizes, so that an assembling operation thereof is troublesome and needs a lot of assembling processes and labors, thereby preventing a production cost from being reduced.
An object of the present invention is to perform an opening and closing operation particularly suitable for an intake valve and a discharge valve in a pulsation type diaphragm pump provided with an intake chamber and a discharge chamber for a fuel, a pump chamber, a pump diaphragm oscillating due to a pressure pulsation generated in accordance with an operation of an engine so as to change a capacity of the pump chamber, a pulsation diaphragm smoothening a pulsation of the fuel generated in the intake chamber and the discharge chamber, an intake valve communicating or shutting the intake chamber with or from the pump chamber, and a discharge valve communicating or shutting the pump chamber with or from the discharge chamber.
Further, another object of the present invention is to reduce the number of parts constituting the intake valve and the discharge valve in the above mentioned pulsation type diaphragm pump and the number of assembling processes and labors therefor.
Further, the other object of the present invention is to make the intake valve and the discharge valve open and close normally for any engines so as to achieve a reliable pump function.
In accordance with the present invention, the intake valve is structured such that a valve seat having a valve seat port for communicating the intake chamber with the pump chamber protrudes into the inner portion of the pump chamber, and a valve body for opening and closing the valve seat port in cooperation with a seat surface of the valve seat is a portion opposing to the valve seat of the pump diaphragm. Further, the discharge valve is structured such that a valve seat having a valve seat port for communicating the pump chamber with the discharge chamber protrudes into the inner portion of the discharge chamber, and a valve body for opening and closing the valve seat port in cooperation with a seat surface of the valve seat is a portion opposing to the valve seat of the pulsator diaphragm.
The valve body of the intake valve is apart from the seat surface in an intake stroke in which the pump diaphragm is displaced in a direction to expand a capacity of the pump chamber, and is brought into contact with the seat surface and seated on the seat surface in a discharge stroke in which the pump diaphragm is displaced in a direction to compress the capacity of the pump chamber. Further, the valve body of the discharge valve is brought into contact with the seat surface in the intake stroke in which the pulsator diaphragm is displaced in a direction to compress the capacity of the discharge chamber, and is part from the seat surface in the discharge stroke in which the pulsator diaphragm is displaced in a direction to expand the capacity of the discharge chamber. As mentioned above, parts of two oscillating diaphragms serve as the valve bodies of the intake valve and the discharge valve respectively, whereby it is possible to properly intake the fuel from the intake chamber to the pump chamber and discharge the fuel from the pump chamber to the discharge chamber.
Further, since the present invention employs the pump diaphragm and the pulsator diaphragm with which the pulsation type diaphragm pump is provided as function parts in the valve body, the number of the parts constituting the intake valve and the discharge valve and the number of assembling processes and labors are reduced, whereby it is possible to achieve a reduction of a production cost.
Further, in order to improve a pump efficiency, the intake valve and the discharge valve are required to be structured such that the valve bodies thereof are completely brought into contact with the seat surface of the valve seat and seated at a time of closing the valves. Accordingly, in the intake valve, it is preferable to eccentrically arrange a diaphragm retainer of the pump diaphragm at a position not overlapping with the seat surface of the valve seat or form the pump diaphragm in a flat surface shape so as to bring it into contact with the seat surface in a flat state. Further, in any one or both of the intake valve and the discharge valve, it is preferable to form the seat surface of the valve seat with an elastic seal member or make the portion forming the valve body of the pump diaphragm and/or the pulsation diaphragm thick in such a manner as to protrude toward the seat surface, or urge a base fabric of the diaphragm to a surface opposite to the seat surface.
Next, in accordance with the present invention, at least one shim is inserted between a peripheral side wall surrounding the pump chamber of the pulsation type diaphragm pump provided with the intake valve and the discharge valve and the pump diaphragm laid over end surface thereof, and/or between both a peripheral side wall surrounding the intake chamber and the discharge chamber and a partition wall sectioning them and the pulsator diaphragm laid over end surfaces thereof.
It is possible to both largely open the valve seat port and completely attach the valve body to the seat surface by adjusting an interval between the seat surface of the intake valve and the valve body and/or an interval between the seat surface of the discharge valve and the valve body by the shim.
Further, in accordance with the present invention, the valve seat of the intake valve and/or the discharge valve is selected from structures having different protruding lengths to the pump chamber and/or the discharge chamber.
It is possible to both largely open the valve seat port and completely attach the valve body to the seat surface by adjusting an interval between the seat surface of the intake valve and the valve body and/or an interval between the seat surface of the discharge valve and the valve body by selecting the valve seat.